Electrostatic lens for magnifying deflection of electron beams or the like



Febl, 1966 HIDEo KuRoDA ETAI. 3,233,144

ELECTROSTATIC LENS FOR MAGNIFYING DEFLECTION OF ELECTRON BEAMS OR THE LIKE Filed Jan. 25, 1963 2 Sheets-Sheet 1 lzzlfl.

Taal. Tucfy Feb- 1, 1966 HlnEo KURoDA ETAL 3,233,144

ELECTROSTATIC LENS FOR MAGNIFYING DEFLECTION OF ELECTRON BEAMS OR THE LIKE Filed Jan. 25, 1963 2 Sheets-Sheet 2 I N VE NTORS ,4f/05a Kupon# ///sA0 739K@ YAM@ BY A//aE/r/ A/oa YA sw United States Patent O 3,233,144 ELECTROSTATIC LENS FR MAGNIFYING DE- FLECTION F ELECTRON BEAMS 0R TIE LIKE Hldeo Kuroda, I-Iisao Takayama, and Hideiri Kobayashi, Tokyo, Japan, assignors to Nippon Eiectric Company Limited, Tokyo, Japan, a corporation oi Japan Filed Jan. 23, 1963, Ser. No. 253,470 Claims priority, application Japan, Feb. 1, 1962, .W7/4,004 8 Claims. (Cl. 315-31) This invention relates to an electrostatic lens for magnifying the deflection of a beam of electrons or other charged particles. The invention is useful in cathode ray tubes or any other device that utilizes a deflectable beam of charged particles.

In order to facilitate miniaturization of television receivers, it is desirable to reduce the. power required to sweep an electron beam across the face of the television picture tube to a level which can be provided by low power transistors rather than high power vacuum tubes. In addition, it is desirable to increase the deflection sensitivity of cathode ray tubes which are used in measuring instruments and in similar devices. Accordingly, several arrangements have been devised in the past to increase the defiection sensitivity of cathode ray tubes. One of these prior art defection magnifiers is disclosed in Japanese Patent No. 14,424/ 1962, entitled A Cathode Ray Tube, and another is described in an article entitled High Speed Oscilloscope With Electron Optical Magnification Using Four-Pole Lenses, which was published in The Review of Scientific Instruments, volume 32, Number 4 (April 1961 on pages 421-424. These prior art deflection magnifiers, however, have several serious shortcomings. The magniiier described in the Japanese patent comprises a diverging lens which contains net-like elements that absorb or scatter portions of the electron beam. The magnifier described in The Review of Scientific Instruments uses a relatively complicated v arrangement of electrodes and magnetic poles which are non-radial in structure. Consequently, the deflection magnification factor is not uniform, but rather varies in accordance with the direction of deection.

Accordingly, one object of this invention is to provide a deflection magnifier which is simpler and more reliable than those heretofore known in the art.

Another object of this invention is to provide a deflection magnifier in which the deflection magnification factor is independent of the direction of deection.

A further object of this invention is to provide a deflection magnifier which is more effective than those heretofore known in the art.

Other objects and advantages of the invention will be apparent to those skilled in the art from the following description of several specific embodiments thereof, as illustrated in the attached drawings, in which:

FIG. 1 is an axial section of a cathode ray tube containing one embodiment of the invention;

FIG. 2 is an axial section illustrating the action of a radial electrostatic lens having a potential ratio in the order of 20 to 1;

FIG. 3 is an axial section illustrating the action of a radial electrostatic lens having a potential ratio in the order of 2,000 to 1;

FIG. 4 is an axial section illustrating the action of a radial electrostatic lens having a potential ratio in the order of 200 to one with a diverging electr-on beam input;

FIG. 5 is an axial section illustrating the action of a radial electrostatic lens having a potential ratio in the order of 200 to one with a converging electron beam input;

f. ICC

FIG. 6 is an axial section of a cathode ray tube containing a second embodiment of the invention;

FIG. 7 is an axial section of a third embodiment of the invention;

FIG. 8 is an axial section of a fourth embodiment of the invention;

FIG. 9 is an axial section 'of a fifth embodiment of the invention; and

FIG. 10 is an axial section of a sixth embodiment of the invention.

The general principles of this invention can best be explained in connection with FIGS. 2 through 5, which illustrate the action of a prior art electrostatic lens under varying voltage ratios and electron beam inputs. Each figure shows two cylindrical electrodes 12 and 14 which are mounted in spaced relation along a common axis C in accordance with well known prior art electrostatic lens principles. Electrodes 12 and 14 are provided with differing potentials to generate an electrostatic lens such as indicated by the solid lines in FIG. 2, which show the distribution of equipotential lines when the potentials of the two electrodes differ by a ratio of around 20 to 1. In all of these figures, the right hand electrode of the pair is at the higher potential. When a diverging electron beam is passed through the electrostatic lens it will be focussed so as to converge at a point P1 by the action of the lens. If the ratio of potentials between the two electrodes is raised to around 2,000 to 1, the electron beam will tirst converge at a point P2 (FIG. 3) within the electrostatic lens and then converge at a second point P3 outside of the electrostatic lens. At intermediate potential ratios, however, e.g. in the order of 200 to 1, the diverging electron beam will converge at a point P4 (FIG. 4) within the electrostatic lens and then diverge at an ongle larger than its original angle of divergence. If the electron beam input is converging rather than diverging, it will be converged twice at points P5 and P6 (FIG. 5 at intermediate potential ratios.

The deflection magnifying action of this invention is based on the refractive action of a moderately strong electrostatic lens such as illustrated in FIG. 4. As shown in FIG. 4, a lens of the type produces a magnification of the .angle of divergence for an elect-ron beam directed along the axis of the lens. Assume, however, that a small electron beam is deflected away from the axis of the lens, e.g. that it is skewed away from the axis C by an angle equal to the angle of divergence of the electron beam shown in FIG. 4. This small, deflected electron beam willact as if it were a part of a larger beam which is directed along the axis C. In other words, the small, deftected electron beam will pass through point P4- and then be deflected in the Opposite direction at an increased angle of deflection, as indicated by the dashed lline B in FIG. 4. If the small, deflected input beam is converging when it enters the electrostatic lens, it will be converged twice while it is being deected after the pattern shown in FIG. 5. In essence, then, this invention resides in applying Ia small deflection to an electron beam entering a moderately strong electrostatic lens which is adapted to magnify angles of divergence as illustrated in FIG. 4. The deflected beam is preferably converging at the input to the electrostatic lens so that it will be focused at a point outside of the electrostatic lens as illustrated in FIG. 5.

FIG. 1 shows one specific embodiment of the invention mounted in a cathode ray tube 16 which contains a cathode 18, a control electrode 20, an accelerating electrode 22, and a focusing electrode 24 for forming an electron beam 26 in accordance with well known prior art principles. The cathode ray tube also contains an electrostatic lens comprising spaced coaxial electrodes 28 and 30, which are provided -with suitable potentials from a source not shown in the drawings to produce a moderately strong electrostatic lens having the divergence magnification properties illustrated in FIG. 4. In addition, the tube contains a low power magnetic deflection system including magnetic pole pieces 32 and 34 and input windings 36 and 38. The magnetic deflection system can be similar to prior art magnetic deflection systems, except with respect to power capacity, which is reduced by the deflection magnifying action of this invention. The magnetic deflection system deflects electron beam 26 from the Iaxis C of the tube structure at the entry to the electrostatic lens, which is formed in the space separating electrodes 28 and 30. The deflection imparted by the magnetic deflection system is reversed and magnified in accordance with the principles discussed above in connection with FIG. 4. At the salme time, the beam itself is converged once within the electrostatic lens and a second time outside the electrostatic lens in accordance with the principles illustrated in FIG. 5. The electron beam then strikes a target ed, which can be a storage screen or a display screen or any other suitable target.

Since the electrostatic lens is radial in this invention, the deflection magnification is the same for every direction of deflection. In this connection, it should be noted that the particular direction of deflection shown in FIG. l would have to be caused by a magnetic field perpendicular to the plane of the drawing, i.e. by a set of pole pierces and windings at right angles to the pole pieces and windings shown in FIG. l. These additional windings and pole pieces are omitted from the illustrations for the sake of simplicity and clarity, since magnetic deflection systems per se are well known to those skilled in the art. It should lalso be noted that the deflection magnifying lens of this invention does not introduce any non-linearities into the deflectien system if its aberration is held to a small value. According to the theory of geometrical electron optics, a strong electron lens with low aberration produces an output deflection angle which is proportional to the input deflection angle. Therefore, the linearity of deflection is not substantially affected by the deflection magnifying lens of this invention. In other words, the linearity of deflection in FIG. 1 is determined solely by the linearity of the prior art portions of the deflection system. In addition, the final focus point of the electron beam in this invention can be determined in a similar way to that of a conventional cathode ray tube, which -rneans that the effective resolution of the cathode ray tube Will also be magnified by the deflection magnifying lens of this invention as long as its aberration is low.

FIG. 6 shows another embodiment of the invention in a cathode ray tube which contains an electrostatic deflection system rather than a magnetic deflection system. In this embodiment, an e-lectron beam 42 is initially deflected by la set of electrostatic deflection plates 44, and the deflection is magnified by an electrostatic lens system comprising electrodes 46 and 4%, which are provided with different potentials from a source not shown to exhibit the divergence magnification pattern illustrated in FIG. 4. The degree of deflection magnification in this embodiment is indicated generally by the difference between the electron beam positions represented by solid lines 42A and 42B and the beam positions represented by dashed lines 42A and 42B', Which show the position of electron beam 42 with and without deflection magnification.

FIGS. 7 and 9 show other electrode structures which can be used in this invention. In FIG. 7, two conical electrodes 50 and 52 are used. In FIG. 9, a cylindrical electrode 54 and a cup shaped electrode 56 are used. Cup shaped electrode. 56 concentrates the electrostatic `field so that the deflection magnification action can be achieved at lower potental ratios.

In the structures of FIGS. 8 and l() an intermediate electrode is added to provide la three-electrode electro static lens system. FIG. 8 shows two cylindrical electrodes 58 and et? and a conical electrode 62. FIG. l0 shows a cup shaped electrode 64, `a cylindrical electrode 66, and a conical electrode 68. In each of these three electrode systems, the potential of the intermediate electrode is preferably lower than the potentials of the other two electrodes, Whose potential is selected to provide the desired characteristics yfor the corresponding electrostatic lens. In all of the above noted embodiments, the electrodes can be mad-c o-f any suitable material, including a conductive film sprayed on the inside of the tribe, and can `he fabricated in accordance with well known .prior art techniques. The potentials can be provided by any suitable prior art potential source.

From the foregoing description it will be apparent that this invention provides a deflection magnifier which is simpler and [more reliable than those heretofore known in the art. it will also be apparent that this invention provides a deflection magnifier in which the degree of deflection magnification is independent of the direction of deflection. And it should be understood that this invention is by no means limited to the specific embodiments disclosed herein, since many modifications can be made in the disclosed structure Without departing from the basic teaching of this invention. For example, the invention is not limited to electron beam devices; it can be used in any device containing `a stream of charged particles other than electrons. These and many other modifications of the invention will be apparent to those skilled in the art, and this invention includes all modifications falling within the scope of the following claims.

What is claimed is:

l. A deflection magnifier for magnifying the deflection of a stream of charged particles which pass along a normal path between a source of said ,particles and a target therefor, said deflection magnifier comprising a single moderately strong electrostatic lens including first and second annular electrodes :spaced from one another along the 4path of said stream and means for applying a difference of potential to said annular electrodes to develop an electrostatic field thereinbetween, said annular electrodes being adapted to receive said stream of charged particles therethrough, deflection means upstream of said lens and immediately adjacent thereto to deflect the path of said stream in accordance with a signal applied to said deflection means, said difference olf potential being of such magnitude as to magnify deflection of said stream of charged particles the deflection magnification of said stream of particles being produced in the region between said electrodes and being maximum in the region furthest downstream from said electrodes, and said deflection magnification ybeing substantially the same for all directions of deflection.

2. The combination defined in claim 1 wherein the ratio of potential lbetween said two electrodes is of the order of 200 to one.

3. A deflection magnifier for magnifying the deflection of a stream of charged particles which pass along a normal path between a source of said .particles and a target therefor, said deflection magnifier comprising a single moderately strong electrostatic lens including first and second electrodes, said first electrode being generally annular in shape and located in the path of said stream, said second electrode being located downstream from said first electrode, said second electrode being generally in the shape of a conical section with its larger end downstream from its smaller end, means for applying a difference of potential to said electrodes to develop an electrostatic field thereinbetween, said electrostatic field being in the path of said stream of charged particles, said difference of potential being of such magnitude as to magnify deflection of said stream of changed particles the deflection magnification o-f said stream of particles being produced in the region between s-aid electrodes and being maximum in the region furthest downstream from said electrodes, and said deiiection magnification. being sul sitantially the same for all directions of deflection.

4. The combination deined in claim 3 wherein the ratio of potential between said two electrodes is of the order of 200 to one.

5. A deflection magniiier for -magnifying the deiiection of a stream f charged particles which pass along a normal .path ibetween a source of said particles and a target therefor, s-aid deection magnifier comprising three stream divergence lmagnifying electrodes, said electrodes being genera-lily annular in shape and mounted in spaced relation along a common axis, means for applying potential differences to said electrodes lto develop an electrostatic field therebetween, said electrostatic iield -being in the path of said stream of charged particles, and said difference of potential `being of suoh magnitude as to magnify deflection of said stream of charged particles.

6. T-he combination defined in claim 5 wherein said common axis lies along the nonmal path of said stream of charged particles and also including means for deecting said stream of ycharged particle-s from said normal path thereof.

References Cited by the Examiner UNITED STATES PATENTS 4/1941 Nicoll 315-31 X OTHER REFERENCES Epstein: Electron Optical System of rIwo Cylinders as Applied to Cathode-R-ay Tubes, Proc. of IRE, August 1936, vol 24, No. 8, page 1108.

El-Kareh: High Speed Oscilloscope Wit-h Electron Optical Magnification Using Four Pole Lenses, The Review of Scientific Instruments, April 1961, vol. 32, No. 4, pages DAVID G. REDINBAUGH, Primary Examiner. 

1. A DEFLECTION MAGNIFIER FOR MAGNIFYING THE DEFLECTION OF A STREAM OF CHARGED PARTICLES WHICH PASS ALONG A NORMAL PATH BETWEEN A SOURCE OF SAID PARTICLES AND A TARGET THEREFOR, SAID DEFLECTION MAGNIFIER COMPRISING A SINGLE MODERATELY STRONG ELECTROSTATIC LENS INCLUDING FIRST AND SECOND ANNULAR ELECTRODES SPACED FROM ONE ANOTHER ALONG THE PATH OF SAID STREAM AND MEANS FOR APPLYING A DIFFERENCE OF POTENTIAL TO SAID ANNULAR ELECTRODES TO DEVELOP AN ELECTROSTATIC FIELD THEREINBETWEEN, SAID ANNULAR ELECTRODES BEING ADAPTED TO RECEIVE SAID STREAM OF CHARGED PARTICLES THERETHROUGH, DEFLECTION MEANS UPSTREAM OF SAID LENS AND IMMEDIATELY ADJACENT THERETO TO DEFLECT THE PATH OF SAID STREAM IN ACCORDANCE WITH A SIGNAL APPLIED TO SAID DEFLECTION MEANS, SAID DIFFERENCE OF POTENTIAL BEING OF SUCH MAGNITUDE AS TO MAGNIFY DEFLECTION OF SAID STREAM OF CHARGED PARTICLES THE DEFLECTION MAGNIFICATION OF SAID STREAM OF PARTICLES BEING PRODUCED IN THE REGION BETWEEN SAID ELECTRODES AND BEING MAXIMUM IN THE REGION FURTHEST DOWNSTREAM FROM SAID ELECTRODES, AND SAID DEFLECTION MAGNIFICATION BEING SUBSTANTIALLY THE SAME FOR ALL DIRECTIONS OF DEFLECTION. 